The present invention relates to a switching amplifier, which amplifies analog signals or multi bit digital signals, and relates to a new switching amplifier in which power supply switching noise is reduced to improve the quality.
A switching amplifier comprising a conventional power amplifier is shown in FIG. 7. This conventional example relates to a switching amplifier for audio. This switching amplifier is provided with an audio power amplifier 1 and a power supply 6, the audio power amplifier 1 being provided with a xcex94xcexa3 modulator 2 for xcex94xcexa3 modulating an audio signal. The construction is such that an output pulse signal from this xcex94xcexa3 modulator 2 is supplied to a power switching element 3 in the amplifier, and then output via an output filter 4 in the amplifier. The power supply 6 is connected to this power switching element 3 in the amplifier, the construction being such that the power supply 6 receives a clock signal, performs pulse width modulation in synchronization with this clock signal, supplies this pulse width modulated signal to a power switching element in the power supply, and supplies required power to the power switching element 3 in the amplifier via an output filter in the power supply.
This conventional example of a switching amplifier operates as follows. Firstly, a signal such as an audio signal or the like is input to the xcex94xcexa3 modulator 2, and a sampling clock is input to this xcex94xcexa3 modulator 2 at the same time. The input signal is xcex94xcexa3 modulated by the xcex94xcexa3 modulator 2, and the output pulse signal thereof is input to the power switching element 3 in the amplifier. In addition, a different clock signal from the sampling clock signal is input to the power supply 6, pulse width modulation is performed in synchronization with this clock signal, and the pulse width modulated output pulse signal is input to the power switching element in the power supply. The output of the power switching element in the power supply is output through an output filter 7 in the power supply, and supplies power to the power switching element 3 in the amplifier.
However, since the power supply 6 and the power amplifier 1 are independent from each other in this method, there is a problem that switching noise from the power supply 6 easily affects the output of the power amplifier. In addition, a large output filter 7 in the power supply must be installed at the output of the power supply so that switching noise from the power supply does not affect the power amplifier 1. However, a conventional output filter 7 in the power supply is typically constructed such that a smoothing circuit and a noise filter are connected, and the installation of a noise filter in this case makes miniaturization difficult. Moreover, if construction of the output filter 7 in the power supply is attempted excluding a noise filter, it is necessary to enlarge a capacitor and a choke coil that comprise the smoothing circuit. Whichever construction is used, since the output filter 7 in the power supply is comparatively large, there is a problem that it is difficult to miniaturize the switching amplifier.
The present invention takes the above problems into consideration, with an object of providing a new switching amplifier that reduces the switching noise of a power supply, in particular to achieve an improvement in quality.
To achieve the abovementioned object, in the present invention, the timing of switching noise in the power amplifier and the power supply is almost the same, and even if noise from the power supply is mixed in, it is possible to use a common noise filter in the power amplifier. Furthermore, a noise filter for power supply is unnecessary, and it is also not necessary to have a smoothing circuit equipped with a comparatively large-sized capacitor and choke coil in the power supply output, so that it is possible to simplify the output filter of the power supply. Moreover, simplification of the power supply output filter enables the switching amplifier to be miniaturized and cost reduced.
That is, the present invention has the following construction in order to solve the above problems.
A switching amplifier according to a first aspect of the present invention comprises: a switching power amplifier which has a modulator which modulates an analog signal or a multi bit digital signal into a two-level signal, and supplies an output pulse signal from the modulator to a power switching element; and a xcex94xcexa3 power supply which has a xcex94xcexa3 modulating device which xcex94xcexa3 modulates an analog signal or a multi bit digital signal, and supplies a pulse signal for power supply control output from the xcex94xcexa3 modulating device to a power switching element in the power supply, wherein an output pulse signal of the modulator in the power amplifier is supplied to the xcex94xcexa3 power supply, and the output pulse signal is input as an operating clock to the xcex94xcexa3 power supply, and the output power of the xcex94xcexa3 power supply is supplied to the power switching element in the power amplifier.
A switching amplifier according to a second aspect of the present invention comprises: a power amplifier having at least a pair of power switching elements in the output stage thereof, which modulates an input signal comprising an analog signal or a multi bit digital signal into a two-level signal, and obtains an output signal power amplified by controlling the conductivity of the power switching elements complimentarily based on the two-level signal; and a switching power supply which generates a required power supply voltage to be supplied to the power switching elements by switching in synchronization with the two-level signal.
A switching amplifier according to a third aspect of the present invention is that, in a switching amplifier according to the second aspect of the present invention, an operation timing between the switching power supply and the power amplifier is set such that noise accompanying the switching operation of the switching power supply occurs within a predetermined period during which the power switching elements installed in the output stage are both off.
A switching amplifier according to a fourth aspect of the present invention is that, in a switching amplifier according to the second or the third aspects of the present invention, the switching power supply comprises a xcex94xcexa3 power supply, which receives the two-level signal as an operating clock signal.
A switching amplifier according to a fifth aspect of the present invention is one where, in the switching amplifier according to the fourth aspect of the present invention, the switching power supply comprises: a voltage converting section having a switching element inserted in a current path of an external power supply, and which converts the voltage of the external power supply into the required power supply voltage by switching this switching element; and a switching control section which xcex94xcexa3 modulates the power supply voltage converted by the voltage converting section, and controls switching of switching elements constituting the voltage converting section based on a signal obtained by this xcex94xcexa3 modulation.
According to the construction of this invention, the switching operation of the switching power supply is synchronized with a two-level signal which controls the conduction of a pair of power switching elements on the power amplifier side, and is synchronized with the switching of these pair of power switching elements. Consequently it is possible to match the timing of noise occurring accompanying the switching operation of the switching power supply with the timing of switching the pair of power switching elements in the output stage, so that the occurrence of switching noise on the output signal appears to be reduced virtually. Furthermore, by adjusting the timing such that noise accompanying the switching operation of the switching power supply occurs within a predetermined period during which the pair of power switching elements is off, noise accompanying the switching operation of the switching power supply does not appear on the output signal via the pair of power switching elements. As a result, it is possible to miniaturize a filter for suppressing noise accompanying the switching operation of a switching power supply or power switching elements.